MEC304 from quizlet Flashcards
What is manufacturing?
Turning raw material into an end product
What is technology?
A piece of equipment
What are systems?
A group of resources
What are the 3 features of technology?
Operating capability - e.g. how large a product
Operating parameters - e.g. how fast cutter goes
Operating costs - e.g. how much energy consumed
What are the manufacturing system demands?
Increased product variety Decreased product quantities Increase in customer expectations Decrease in time to market Use new or better materials Facilitate global production
What are physical structures?
Factories, equipment etc
What are virtual structures?
Management and control systems
What are the 5 P’s of product and operation management?
Product Plant Process Programme People
What is the Product?
The interface between marketing and production
An agreement must be reached on performance and aesthetics, quality and reliability, quantity, selling price/production cost and delivery date/lead time
What is the Plant and what must it do?
Provides the tools to manufacture the product
It must match all needs and continue to do so
Must consider possible future demands, layout of buildings and facilities, performance and reliability of equipment, maintenance, safety and social responsibility
What is the Process?
The combination of people, skills, and equipment to manufacture the product
To optimise consider available capacity and skills, form of production, plant layout, safety and maintenance, costs
What is Programme/Resource Plan?
System which organises and controls the production operations.
Generates timetables and procedures for purchasing, production, maintenance, cash flow, storage and transport
What is People?
Link the virtual and physical structures
What is High Value Manufacturing (HVM)?
As the UK cannot compete on volume manufacturing, they try to compete by adding value to manufactured goods through technological improvement
What are the 3 key demands on HVM?
Reduced product quantities
Increased customer expectations
Use of new or better materials
How does HVM generate jobs?
It requires new processes to be developed and enables supply chains to be brought closer to production facilities
What is Industry 4.0?
Applying emerging digital technologies to manufacturing in order to improve productivity and quality and reduce costs
Who will industry 4.0 impact?
Basic manufacturing processes
What is Machining?
The process of removing unwanted material from a workpiece in the form of chips
What are examples of traditional casting?
Disposable mould casting such as sand or investment casting
What are examples of recent casting developments?
Permanent mould casting, powder metallurgy, additive manufacturing
What are examples of traditional machining?
Turning, milling, drilling, boring, sawing, grinding, polishing
What are examples of recent machining developments?
High speed machining, grinding, electrical discharge machining
What are examples of traditional joining?
Fusion welding, brazing, soldering, mechanical fastening
What are examples of recent joining developments?
Electron/ laser beam fusion welding, resistance/spot welding, solid state
What are examples of machining inputs?
Machine tool, cutting tool, workpiece properties, cutting parameters, workpiece holding device
What are machine tools?
Manual lathes and milling machines
What are cutting tools?
Consumables required for machine tools
What are one-piece cutting tools?
Traditional solid cutting tools
What are modern two-piece cutting tools made of and why is this beneficial?
Made of an insert and a body, allowing each part to have different properties and use more exotic materials. Also cheaper as only warn parts need replacing.
What are the mechanics of chip formation?
Tool moves along shear plane at cutting speed v
A clearance angle exists to minimise contact between tool and workpiece
Shearing occurs at shear plane and material above the shear plane forms chips
What are 3 cutting parameters?
Speed - velocity of tool relative to workpiece
Feed rate - velocity perpendicular to speed
Depth of cut - how far tool penetrates per cut
What is the Material Removal Rate (MRR) equation for single point tools and multi point tools
Single point tools - speed x feed x depth of cut
Multi point tools - Cross-Sectional Area of cut x feed
What are the 4 types of chip?
Continuous
Serrated
Discontinuous
Built up edge (BUE)
How are continuous chips formed?
Ductile materials, high cutting speeds
Deformation of material along primary shear zone
Good surface finish but need chip breakers to prevent wrapping around tool
How are serrated chips formed?
Zones of high and low strain
Saw-tooth-like appearance
Metals with low thermal conductivity and strength that decreases with temp
How are discontinuous chips formed?
Segments that may be firmly or loosely attached
Brittle materials
Extreme low or high cutting speeds, deep cut
Poor surface finish and accuracy
How are BUE chips formed?
Formed at tool tip during cutting
Layers build up on tool then break off
Poor surface finish and work hardening of surface
What are the two main strands of development?
Application Specific
Process Specific
What is the application specific strand of development?
To enable machining to be used to create a component that was previously impossible
What is the process specific strand of development?
Enables tools to operate further beyond their original parameters to improve productivity
What are the advantages and disadvantages of High-Speed Steel (HSS) tools?
+cheap
+easy to shape
+easy to resharpen
+can be coated to improve durability
-wear away quickly
What are the advantages and disadvantages of Tungsten Carbide (WC) tools
+cheap as inserts
+easy to shape
+good abrasion and heat resistance
+maintain cutting edge at higher speeds and temps
-more expensive than HSS
What matrix’s do ceramic composites have? What are the advantages and disadvantages of ceramic composite tools?
Aluminium oxide or silicone nitride as a matrix
+improved heat resistance over carbides
+no need for lubricant/coolant
-more brittle so suddenly fail
What is the role of process modelling?
It is often very expensive to trial and error so modelling is used to predict the outcome of a particular process
How are processes modelled?
Database is used to process information
Modelling is completed based on the database
Simulations are performed based on models
Intelligence is used to utilise simulation results
What are the uses of process modelling?
Optimise process parameters
Prediction of tool life, geometrical accuracy of parts, surface finish, chip control, loads on workpiece
What are the types of process models? (Three types)
FEM to analyse tool and material stresses
Thermal models to analyse impact of heat
Matlab models to analyse dynamic effects
What are free vibrations in machining?
Result from impulses transferred to the machine structure
Can be caused by initial engagement of cutting tool or rapid reversal of masses
What are forced vibrations in machining?
Result from external periodic forces acting on the system
Can be caused by unbalanced shafts, periodic components of cutting forces or other nearby machines
What are self-excited vibrations in machining (chatter)?
Result from dynamic instability in the workpiece interaction
Caused by large tool engagements which cause oscillations to build up
Why is chatter bad?
Causes poor surface finish (waves)
Unstable cutting breaks tools
Lowers productivity as cannot operate at optimum parameters (need do decrease speed, feed or depth)
How do you control free vibrations, forced vibrations and chatter?
Free vibrations - sensible operations
Forced vibrations - good maintenance and careful positioning of machines
Chatter - Optimise process parameters
What causes self-excitation (chatter)?
Mode coupling - relative motion between tool and workpiece in at least 2 directions causing periodic elliptical motion of the tool tip
Regeneration of surface waviness - when tool tip moves over the surface already cut and the next pass of the tool creates a wavy surface again
What are the benefits of modelling self-excitation?
Based on mass spring damper system
Allows selection of process parameters in real time
Can cut at higher speed and depth to be in stable region
Increased productivity
How do you control self-excited vibrations?
Add more damping or stiffness to structure to ensure major vibration mode doesn’t coincide with cutting forces
Add tuned mass-spring system with natural frequency coinciding with major vibrational mode
Use special cutters with non-uniform teeth spacing
Use actuator to provide large damping force
Use long vibrating tools to damp the tooling
What is inspection used for?
Used for acquiring data for quality control, providing data for the design process and acquiring data for legal obligations
What is inspection, in particular for machining, needed for?
Process control - Selection of cutting tools and parameters
Acceptability and conformance - helps maintain preferred supplier status
Post-assembly performance - informs assembly process as to whether performance requirements are met
What is metrology?
The science of measurement used to perform most inspection by hand
What are Coordinate Measuring Machines (CMM) used for?
Measure how accurately a part has been produced to the specification
What are the advantages and disadvantages of CMM?
+Very accurate
-Very slow as time is needed between touches for vibrations to dissipate
What are the 3 main parts that make a CMM?
Support Structure
Probing System
Data Acquisition
What is the CMM Support Structure?
Provides solid frame and motion to the probes in up to 3 axis
Base usually made of cast granite
Drive structure usually made of extruded aluminium
What is the CMM Probing System?
Probe is usually a very hard ball such as ruby
Applied to the surface being measured
Is spring loaded and deflections provide data
What is the CMM Data Acquisition?
Machine controller and hardware/software to record deflection of the probe
What is the accuracy of CMM like?
CMM can be very accurate if probes are calibrated properly and approach surfaces at angles to minimise skid
What are the factors that can maximise the accuracy of CMM?
Strength, stiffness and mass of machine
Thermal stability of machine (changing size)
Smooth drive system
Software to compensate for geometric and thermal error
Want errors to be systematic
How are systematic errors of CMM handled?
Measure errors on each CMM
Calculate correction values and store
Apply correction values with controller software
Verify CMM performance
How can CMM be improved?
Minimise movement in linear axes by introducing spherical movement of head, minimising vibrations
What is Additive Manufacturing (AM)?
A family of automated technologies used to create physical parts, layer by layer from 3D CAD files
How has the use of AM technology evolved?
Rapid prototyping - plastics with poor properties
Rapid tooling - producing mould tools
Rapid manufacturing - achieving useable parts
What is the Stereolithography (SLA) method?
Laser scans a tank of liquid photopolymer and locally cures it layer by layer
Create thermoset polymer parts
What are the advantages and disadvantages of Stereolithography (SLA)?
+Good precision and surface finish
+Wide selection of material characteristics
+Quite fast and can create large parts
- Limited to prototyping or indirect tooling
- Limited to brittle photopolymers
What is the laser sintering method (SLS/DMLS)?
Scanning laser locally sinters powder together layer by layer
Sintering mean fusing together not fully melting
SLS - Polymers
DMLS - Metal alloys
What are the advantages and disadvantages of SLS?
+Can generate complex geometries
+Good mechanical properties
+Good for producing single parts
+Easy post processing
-Can be slow with complex geometries
What are the advantages and disadvantages of DMLS?
+Finished parts have no thermal residual stresses
+Denser than investment cast parts
- Less dense than selective laser melting
- Surfaces have porosity that needs sealing
What is the Fused Deposition Modeling (FDM) method?
Uses coils of solid polymer wire fed through a heated extrusion head and into layers
What are the advantages and disadvantages of FDM?
+Can be very cheap
+Can be quite fast
+Range of machine sizes
+Wide range of polymers
- Can struggle with complex geometries
- Layers usually visible
- Post processing sometimes tricky
What is the 3D printing (Colorjet) method?
Core material spread in thin layers, binder selectively jetted from inkjet style print heads solidifies core material
What are the advantages and disadvantages of Colorjet?
\+Many colours \+Reasonably quick \+Minimal post processing \+Complex geometries \+Cost effective for one off models
- Poor mechanical properties
- Brittle
- Grainy surface before post processing
What are the 4 types of prototypes?
Visual aids
Presentation models
Fit and assembly models
Functional models
Why use rapid prototyping?
Prototype early and often to reduce risk Avoid chance of designing errors Allow early product assessment without tooling Allow creative ideas to be explored Reduce time to market
What are the rapid prototyping processes for polymers?
SLA, SLS, FDM, DLP printing, Polyjet
What is DLP Printing?
Similar to SLA but uses a projected image produced by a DLP projector
Each layer is made up of black white or grey regions
White parts cure, black parts don’t
What are the advantages and disadvantages of DLP printing?
+Better suited to office environments due to no laser
+Faster and uses less material
- More expensive
- Smaller build volume
What is Poly Jet and what are the advantages?
Similar to SLA in that it uses photopolymer resins but the resin is printed by depositing droplets onto a build bed which cure as they are deposited
+Faster than SLA for small builds
+Can produce higher precision and a wider variety of colours
What are the rapid prototyping processes for metals?
DMLS, SLM, EBM
What is Selective Laser Melting (SLM)?
Similar to DMLS but particles fully melt and solidify
What are the advantages and disadvantages of SLM?
+Improved mechanical properties
+Less susceptible to cracking due to greater density
- Need processing to remove residual stress
- Limited to mono materials so all melt at once
What is Electron Beam Melting (EBM)?
Similar to SLM but uses an electron beam to melt powder in a vacuum at high temperature
What are the advantages and disadvantages of EBM?
+Beam can scan more quickly than a laser
+Finished parts free from residual stresses
+Finished parts are fully dense
-Expensive and poor initial surface roughness
What is AM tooling?
Historically mould tools were made by hand which was an expensive and time consuming job, now AM can be used for rapid tooling
What is indirect tooling and what is it good for?
AM techniques used to make moulds that are then used to make the direct mould for non AM processes
Good for complex geometries
What is direct tooling?
AM techniques that are used to make the final mould tool directly to be used in non AM processes
What is soft tooling?
Tools made from soft materials which are cheap and good for non-functional models that are quick to make
What is hard tooling?
Tools made from hard materials which can take advantage of complex hidden geometries
What is bridge tooling?
Used for hard direct tooling of products made from soft materials
What is indirect SLS?
Steel particles coated in polymer binder
Laser scans and selectively sinters binder together
Excess powder removed to lave green part
Furnace to run out binder and sinter steel particles
Can be used on sand particles to make moulds
What is job production?
A task is handled by a single worker or group of workers
Resources are allocated for the duration of the project
Each project is normally a one off
Cost of production includes design, tooling, materials, productions
What is batch production?
Manufacture standardised products in a batch
Skilled and specialised workforce
Machines arranged in functional/ process groups
Jobs move in batches
Large storage areas for WIP
What are Working In Progress (WIP) used for?
Used to cope with market fluctuation, assist in utilising limited resources and take advantage of common parts/ processes
What is the batch production process?
- Breakdown product into production operations
- Determine a batch size
- Machines are set up
- Individual parts in each batch processed
- When all parts completed, batch moves on
What is flow production?
Products manufactured in flow lines
Used for high volume standard products
Factory equipped with dedicated production process
Production is simplified to reduce costs
What is the flow production process?
- Processes separated into equally timed operations
- Raw material processed at first workstation
- Partially completed part moves onto second operation
- First workstation repeats its operation on new material
- Part moves sequentially through all workstations until product is complete
What are the advantages of flow production?
Can cope with high volumes Quality of product traced with in line inspection Automation reduces direct labour Lower labour skill level Reduced inventory Very high machine utilisation
What is process planning?
It is a function in a manufacturing facility that determines which processes are to be used produce the final parts
What is a process plan/job sheet?
Details what features are to be manufactured, what tools are to be used and how long each feature will take to make
What is the geometry analysis procedure in process planning?
- Identify manufacturing features
- Relate geometries to each other
- Determine optimum access or approach direction
Why does the purchasing of raw materials need to be planned in process planning?
Raw material can only be purchased in limited shapes and dimensions so consider waste minimisation and geometry of part
Name and describe the 2 types of process selection in process planning
Gross planning - Select type of process to be used and the specific requirements of each feature considering volume vs cost
Detailed planning - Select tool and process parameters
Why is set up and fixture planning required in process planning?
Position workpiece to allow clear tool paths and group features based on approach directions to minimise repositioning
What happens in analysis and evaluation in process planning?
Evaluate each plan against machining time, cost and quality
What is Computer Aided Process Planning (CAPP) used for?
Computer aided process planning is used to handle the complex planning process
What is the variant CAPP process?
- Existing components analysed, classified and grouped
- Standard plans created for each of the groups
- Similar parts identified and standard plans are edited to suit each part
- New components planned based on standard plans
What are the advantages and disadvantages of variant CAPP?
+Simple to setup and operate
+Planner has control over final process plan
- Planning limited to components previously planned
- Experienced process planners required
- Detailed process plans cannot be generated
What is generative CAPP and what is the process?
Automatic synthesis of a plan for a new part
- Knowledge of manufacturing is captured and stored in a database
- Decision making process is imitated by logic
- Machines and tool elected from logic
- Iterate to optimise
What are the advantages and disadvantages of generative CAPP?
+Generates consistent process plans
+New components can be planned easily
+Easy to integrate with other CIM elements
- Expensive and time consuming to implement
- Needs large database or capability
- Reliant on high quality data
What is process scheduling?
Determines the implementation plan to be used, consisting of time schedule and dispatching sequence
What data is needed for scheduling?
Jobs - due dates, processing times, materials
Activities - expected duration, desired completion
People - availability, capabilities, salary
Plant - machine capability, costs, availability
Facilities - costs, capacity
What is the level of scheduling required for continuous and discrete flow production?
If continuous limited scheduling required
If discrete also limited as product paths are the same
Complex to set up but simple day to day
Why is scheduling required for batch production?
Schedule to minimise risk of running out of inventory
Economic order quantity - Schedule batches to balance production, storage and changeover costs
Run out time - Schedule batches based on the rate the inventory is being used up
How easy is job production to schedule?
High variety so most difficult to schedule so use forward job searching or backward job searching
What can scheduling criteria be used as?
Can be used as performance metrics to aid optimisation e.g. required lead time, required cost
What is the dispatching rule for earliest due date? When is it used?
Jobs scheduled in increasing time left before their due date
Used when due dates change frequently
Ignored processing time so can make jobs static
What is the dispatching rule for shortest processing time? What is it good for?
Jobs scheduled in increasing order of processing time
Good for minimising WIP
What is the dispatching rule for largest processing time? What is it used for?
Jobs scheduled in decreasing order of processing time
Used for minimising impact of long jobs going wrong at the expense of WIP
What is the dispatching rule for the critical ratio?
Jobs scheduled based on current ratio between time until due date and processing time left
Jobs with lowest ratio scheduled first
Prioritises jobs with high chance of being late
What is forward scheduling? What type of job is it suited to?
Start as soon as the process is planned
Suits jobs made to order otherwise build up of WIP and inventory of product
What is backward scheduling? What type of planning does it suit?
The arrival time at the customer site is calculated as the earliest possible goods receipt time at the customers unloading point on the requested delivery date
Rest of the operations are offset one at a time in reverse order
Suits the material requirement planning (MRP) environment
What is the plant layout?
How the physical structures of a manufacturing organisation are arranged on a manufacturing site
What is the process related criteria for a good plant layout?
- Maximise flexibility of machines and layout
- Maximise the use of volume
- Minimise distance and handling of parts
- Efficient and smooth process flow
What is the people related criteria for a good plant layout?
- Maximise coordination between departments
- Maximise visibility of people and materials
- Maximise accessibility of machines and parts
- Minimise discomfort
- Maximise security and safety
What are the advantages of a good plant layout?
\+Minimise process cost and time \+Reduced movement and handling of parts \+Simplified supervision and control \+Accommodate changes readily \+Max output for space and resources
What is the 5S methodology?
Sort - remove unnecessary items
Set in order - set necessary items in the order they are used
Shine - tidy/clean work environment, prevent deterioration
Standardise - common processes, everything in its place
Sustain - regular audits, training, self discipline
What are the two types of layout and what types of production are they used in?
Process layout (Functional layout) - Facilities are laid out by their process type, irrespective of what is being manufactured. Typically used for batch and some types of job Product layout - Facilities are laid out by the requirements of the products that are being manufactured. Typically used in flow
What are the advantages and disadvantages of process layout?
+Flexible use of equipment and workforce means can cope with changes and breakdowns
+Low investment cost as it does not need expensive automation
+Specialised supervision means experts on shop floor can resolve issues quickly
- Large volume of WIP
- Complexity in production planning and control
- Long production time
- Require higher skill level of workforce
What are the advantages and disadvantages of product layout?
+Minimal WIP
+Operations are in planned sequence (simple)
+Short production time as resources are optimised
+Lower skill level of workforce required
- Lower flexibility
- Production pace set by slowest operation
- One machine failure halts production
- Expensive automation
What are the limitations of using a process layout?
- Large volume of Work In Progress (WIP)
- Complexity in production planning and control - different work need different tools, time, people…
- Long production time - Time wasted by moving parts, waiting for machines & people, and setting up each process
- A higher skill level is required of the workforce - Requires flexible, multi-skilled, motivated people
What are the limitations of using a product layout?
- Minimal Work In Progress (WIP) - Less material handling minimises risk of damage. Minimise storage costs and cash tied up in WIP parts
- Operations are arranged in a planned sequence - Simplified planning, control & supervision
- Short production time as all resources optimised
- A lower skill level is required of the workforce - Lower labour and training costs
What does Group Technology (GT) do?
Seeks to make use of geometric and manufacturing similarities among parts
What is cellular manufacturing?
Extends group technology using machine cells (groups of machines) and automation of loading and unloading parts, tool changes, workpiece transfer
What are the advantages of group technology and cellular manufacturing
+Standardised part design saves time and effort
+Facilitates product development as costs are easy to estimate
+Reduced setup with effective planning
+Standardised tools and jigs
+Reduced part movement minimises risk of damage
+Reduced WIP
+No mundane jobs for employees (satisfaction)
What are the disadvantages of using group technology?
Complex to schedule jobs - scheduling a large variety of parts is very complex
What are flexible manufacturing systems?
Extended cellular manufacturing by linking multiple cells together comprised of workstations with automated tools, automates material handling devices and control systems
What are the benefits of flexible manufacturing systems?
+Parts can be produced randomly at low unit cost
+Direct labour and inventories are reduced
+Improved productivity with high machine utilisation
+Reduced production lead time
+Reduced WIP
What is Computer Integrated Manufacturing (CIM)?
A network of computer systems tied together by a single database to control all aspects of a manufacturing system which is used to maximise production capacity and cost effectiveness
What are the subsystems of CIM?
Business planning and support Product design Process planning and scheduling Process control Shop floor monitoring Process automation
What are the advantages and disadvantages of CIM?
+Responsive to shorter product life cycle and changing market demand
+Emphasis on product quality and uniformity
+Better resource utilisation
- Expensive
- Long introduction period
- Benefits not always immediately visible
What is an assembly operation?
An operation that joins two or more components to form a product either permanently or semi-permanently
What are the methods of permanent joining?
Welding
Brazing
Soldering
Adhesive bonding
What are the methods of semi permanent joining?
Standard fasteners - screws, bolts, nuts etc
Specials - snap-lock, uni-directional etc
Need different processes
What are manual assembly lines widely used today for in manufacturing?
Automobiles and trucks
Electronic products
Appliances
Pretty much anything made in large quantities
What did the automation of assembly lines introduce?
Introduced semi-automated technologies to assist workers by reducing fatigue, improving health and safety and increasing quality
What are the reasons for automation of assembly lines typically only being between 30%-50% of the total work content of an assembly line?
Economic - commercial viability vs. labour cost
Flexibility - balance between human and machine. Robots can be very flexible, but still need programming to be so
Process development - humans can innovate
Safety - human/robot interaction (or not!)
How are single component products manufactured?
Often a single or small number of operations that are not dependent on each other. They can be performed by a single machine or multiple dedicated machines.
How are multiple component products manufactured?
Normally need a particular sequence of operations, made on an assembly line from many single component products.
What is the processing time?
Time that workers spend doing stuff to the product at each workstation including waiting time
What is the repositioning time?
Time spent moving parts, tools, people
What is the work content?
Sum of all processing and repositioning time
What is the waiting time (idle time)?
Time one workstation waits after completing its processing and repositioning and is waiting for operations at the next workstation
What does the term ‘bottleneck’ always refer to?
A process restricting production
Where is the bottleneck in push production?
The bottleneck would be said to be at ‘x’, with waiting time at ‘y’, because ‘x’ is delaying production
Where is the bottleneck in pull production?
The bottleneck would be said to be at ‘y’, with waiting time at ‘x’, because ‘y’ is delaying production
What is the manufacturing lead time?
Total time for a single product to be manufactured start to finish
What is the working time available?
The total time available on a line after planned maintenance, shift change, machines startup/shutdown etc
What do precedence diagrams do?
Illustrate the sequence of steps required to make a product
What is lag?
When a deliberate delay is placed between two activities
What is lead?
When subsequent activities begin before the preceding activity finishes
What does float do?
Provides flexibility in workflow/ schedule
What is the total float?
The amount of time an activity can be delayed from its start without delaying due date
What is free float?
The amount of time an activity can be delayed without delaying the early start date of the following activity
What is the ideal cycle time?
How often a product needs to be completed to achieve customer demand
What is the actual cycle time?
How often a product is actually completed
What is the Required (Ideal) or Actual Position Rate?
The cycles per unit time
What is the ideal number of workstations?
Number needed on the line to run at the ideal cycle time
What is the actual number of workstations?
Number needed on the line to run once all inefficiencies have been taken into account
What is the definition of line balancing?
The attempt to balance the operations at various stages of a flow line in order to ensure even loading at each stage, minimise job complexity and minimise bottlenecks or under utilisation
What is the line efficiency?
Ratio between actual and ideal operating time, measuring typical time lost due to breakdowns, power cuts etc
What is the balancing efficiency?
Measure of the total idle time using the ratio between ideal time needed and actual time needed to produce a single product
What is Just In Time production (JIT)?
Just in time is a pull system where components are made to specific orders, generated by a void created when a component is finished
Eliminating unnecessary resources (waste) throughout production, increasing efficiency and making production lean
What are the benefits of a pull system?
\+Flow of information is restricted, giving clarity \+Batch sizes reduced \+Bottlenecks eliminated \+Waiting time of parts is reduced \+WIP reduced \+Reduced set up time
JIT seeks to reduce ‘waste’ by aiming to have…
Zero defects Zero inventories Zero setup times Zero handling Zero breakdowns Zero lead times A batch size of one
How is JIT achieved?
Modular design using existing components
Use existing subassemblies for new products
Group technology and cellular manufacturing
Reduce setup and WIP
Cultivate good supplier relationships
What is Kanban?
Used to control JIT and uses Kanban cards
What is the Kanban setup?
WIP exists between workstations to hold parts
Parts are in standard containers holding a standard number
Kanban cards authorise the movement of parts
How does single card Kanban work?
If you are at a workstation and complete your task but the next workstation has not then they cannot authorise the movement of the container so it goes into the holding area
When the next workstation finishes they take the container and pass you the Kanban card meaning you can take the container from the previous holding area and pass your Kanban card to them
What are the two different cards used in dual card Kanban?
C Kanban - authorises movement (as in single card) to/from that workstation
P Kanban - authorises production to begin in that workstation
What are the rules for dual card Kanban?
C or P Kanban will be attached to all containers except for the one that is in use
No container can be moved without the C Kanban
Standard containers will be filled when P Kanban authorises
P Kanban is attached to a container when it is filled
How do you calculate how many Kanban cards are needed in a system?
y = DT(1+x)/C
no.=(demand per unit timelead time (1+safety factor))/parts per container
What is inventory management used for?
The use of inventory to maintain supply levels, benefit from economies of scale by bulk buying, helping to cope with uncertainty
What does Materials Requirement Planning (MRP) do?
Addresses problem consistent and predictable orders to maintain inventory by considering firm orders and future requirements based on sales forecasts. Typically performed by software.
What are the aims of MRP?
Reduce inventory to a minimum
Aid planning of manufacturing and timely delivery
Ensure resources are there to meet customer demand
What’s the input data required for MRP?
What and how many are being created How long materials can be stored for What materials are available to use Bill of materials for each product Production planning details for each product
What are the outputs produced by MRP?
Recommended production schedule - start/stop dates, quantities
Recommended purchasing schedule - when materials need delivering + purchases need producing
What’s the MRP procedure?
- Gross requirements are noted
- Net requirements are calculated taking account of on hand stock, orders due and safety stock
- Planned orders are net requirements offset by lead time
What is the safety stock?
Stock stored for emergencies but is always included in calculations as it is used and replaced immediately
What are the limitations of MRP?
No consideration of finance or personal required and does not take production capacity into account
What is Manufacturing Resource Planning (MRP II)?
An extension of MRP to plan for manufacturing capacity which take the master production schedule and examines available resources to check feasibility
What does Enterprise Resource Planning (ERP) do?
Integrates a range of activities and information to support all operations, covering the issue of MRP being dumb to what is happening in the rest of the business
What are the advantages and disadvantages of ERP?
+Integration minimises loss of important info
+Better view of business means its easier to make decisions
+Can reduce lead times through better process control
- Expensive and time consuming to implement
- Problems with sharing complex and sensitive data
What is Quality Assurance (QA)?
A system for preventing defects, making sure products are fit for purpose, minimising mistakes and minimising wastes
What is the QA process?
- Examine current product/ process
- Establish test methods and performance metrics
- Identify areas to improve
- Re design
- Re examine new product process
- Repeat
What is Quality Control (QC)?
A system for detecting defects in a product by implementing test methodologies to detect magnitude and frequency of defects. Information is then used to accept or reject the product
What is meant by Kaizen/Continuous Improvement?
All employees engaging in continuous improvement and using their expertise to look at their own work area
What are the aims of Kaizen?
Improve process and product quality
Reduce set up time
Reduce inventory
Reduce material handling
How does Kaizen work?
Well understood by employees as it relates directly to their daily work
Should receive recognition
Over time culture of the company will change
How does Six Sigma improve quality?
Improve quality by identifying and removing the causes of defects, using specially trained workplace champions to implement throughout an organisation
What is the aim of Six Sigma?
To achieve an error rate of 3.4 defects per million opportunities (DPMO)
Ultimately reduce occurrence of defects and achieve lower costs
How do you calculate Defects Per Million Opportunities (DPMO)?
(1,000,000 * no. of defects)/(no. of units * no. of opportunities per unit)
What did Taguchi introduce?
Introduced methods of handling variation within quality based around 3 elements:
- Minimise loss to society due to poor quality
- Customers lose money
- Manufacturers lose reputation
What does the Taguchi loss function do?
Qualitatively describes the loss to society
What does offline quality control do?
Ideally eliminate production variation at 3 stages:
- System design - generate simplest design
- Parameter design - select sensible values
- Tolerance design - consider effect of potential variation of each parameter
Lean manufacturing is concerned with waste elimination in 4 aspects, which are…
Concerned with waste elimination in four aspects:
- Lean plant
- Lean supplier network
- Lean production development
- Relationships with distributors and customers
What does a lean plant do?
Optimise factories and machines
Make use of automation
Eliminate waste within and between departments
What does a lean supplier network do?
Provide suppliers with incentive for improvement
Promote learning mechanisms among suppliers and workers
Encourage competition
High degree of outsourcing enables companies to cope with changes
Lean product development is different from the traditional approaches on four dimensions, which are…
Leadership - Flat management structure where leaders have authority to make big decisions
Teamwork - All departments share information to avoid duplication of work
Communication - Clear communication between departments
Simultaneous development - Develop and refine designs as you progress
What is agile manufacturing?
Concerned with fast moving, adaptability and robustness
Rapid reconfiguration of manufacturing systems
Integration of technology, organisation and people
What are the characteristics of an agile enterprise?
- Customer centred process
- Functional decision making - decision making by individual units
- Stable unit cost - regardless of volume
- Flexible manufacturing - ability to increase or decrease volumes at will
- Modular production facilities
- Updated data - information used to rapidly improve product knowledge
What are the differences between agile and lean manufacturing in terms of production line, organisation and organisational structure?
Agile determines new solutions rather than improving solutions
Agile rapidly forms multi alliances rather than using enterprise collaboration
Agile has a dynamic organisational structure rather than using flat teams
What is virtual manufacturing?
Combining several physical production systems into one virtual production system regardless of geographical location, ownership or previous supply chains, promoting agility and leanness
What is e-manufacturing?
The utilisation of internet and tether free technology to promote continuous, seamless, synchronised communication between suppliers, plants and customers
What are the advantages of e-manufacturing?
Allows easy sharing of resources and information
Computing infrastructure leased to reduce capital expenditure
Allows easy scaling
Companies pay for what they use
What is global manufacturing?
Moving away from independently managed businesses serving local markets to an international network of businesses serving the distributed markets - built on foundation of lean
